Hydropower Storage Solutions

The two projects recently received funding from the Norwegian Research Council’s large-scale program for energy research ENERGIX. Launched in 2013, the NOK 4 billion program over ten years is the council’s single largest initiative. Improved utilization of resources using balancing power is just one of six focus areas under ENERGIX.

Hydropower storage is an important issue for the industry because it can be help Europe meet the challenge of integrating variable renewable power, like wind and solar, into the power system, according to Ane Torvanger Brunvoll, ENERGIX program coordinator. Using highly controllable hydropower as a substitute when the wind is not blowing and the sun is not shining can increase the revenue for Norwegian power and grid companies

“These projects are particularly relevant since one develops a roadmap towards realizing Norway’s potential for providing hydropower flexibility, while the other explores a novel and important concept for implementation,” says Brunvoll.

HydroBalance II

Research organization CEDREN (Center for Environmental Design of Renewable Energy) started work in September 2013 on HydroBalance phase II, a NOK 24.8 million project on large-scale storage and balancing services of hydropower, set to run four years. The new project is a follow-up to its NOK 4 million predecessor that focused on the potential need and challenges of Norwegian hydro storage for balancing Europe’s growing wind power production and other non-regulative energy sources.

The basic premise is that when wind power plants produce more energy than Europe needs, the excess energy can be used to pump water up to large existing reservoirs in Norway. When there is too little wind, the elevated water can be used to supply power to Europe.

The initial study (Phase I) focused on the potential for balancing and energy storage in the Norwegian hydropower system and the implications of hydropower operation for social acceptance, local communities and stakeholders, and water level fluctuations in reservoirs. The study screened southwest Norway for potential sites for upgrades of existing power stations and installation of pumped storage hydropower plants.

“The main scenario of the study could show that the Norwegian hydropower capacity could be increased by a combined power output of 20 GW, given that current operation and stipulations on reservoir levels would be retained and an environmentally acceptable maximum rate of change in water levels would apply,” says Julian Sauterleute, researcher at SINTEF Energy Research.

International Expertise

Phase II of the project will be significantly larger in scope than its predecessor and include big international project partners, such as French power producer EDF and German utility E.ON. They will contribute with their expertise in grid analysis and business models, among other things. The other industrial partners are Agder Energi, BKK, Energi Norge, Statnett, Statkraft, Sira-Kvina Kraftselsskap, and Listerrådet, all of whom also participated in phase I.

HydroBalance II will take into account the environmental, political, technical and economic aspects of building balancing hydropower power stations. The project has been divided into six work packages. The aim is to create a roadmap for harnessing the flexibility of the Norwegian hydropower and pumped storage to provide balancing power and energy storage in an integrated European energy system.

“The project will draw a picture of the future for hydropower flexibility towards 2050 and assess needs for flexibility, alternatives to hydropower and required transmission capacity,” says Sauterleute. “How can and should the hydropower sector respond to the power system development in Europe?”

Subsea storage power

Another way to harness the immense electricity storage potential of hydropower is to build storage power stations underwater. Subhydro, a Norwegian company founded by German inventor Rainer Schramm, has received funding from ENERGIX to test its subsea pumped hydroelectric plant concept.

The idea works much the same as an onshore hydropower plant that takes advantage of the pressure difference between the lower and upper water reservoirs using a turbine to produce electric power. Subhydro instead utilizes the subsea water pressure to run a subsea turbine at a water depth of 400-800 meters below an offshore wind turbine. The water passing the turbine then goes into large storage tanks. The tanks are connected to the sea surface by pipeline to avoid compressed air.

When the wind speeds are strongest, the excess energy is used to pump water out of the tanks, and thus charge the system. As wind subsides, the stored water can be released in a rush through turbines that can produce electric power. This can be used both to make wind power more stable, but also to possibly electrify nearby offshore oil and gas platforms in the future.

Subhydro said its system could give customers a low cost grid storage solution that is comparable in capital costs to existing onshore hydropower plants. Plus it offers the potential benefit of reducing CO2 emissions in the offshore oil and gas industry, which typically relies on gas turbine generators.

The company believes its technology offers gigawatt hours of storage on a 100-1000 MW scale at over 80% round trip efficiency, dependent on available water depth. The plant will also be more effective the more tanks and the deeper the waters. The greater the pressure difference between the sea surface and the seabed, the more energy can be stored in a single tank.

The goal of the ENERGIX study with Subhydro is to design tanks that are five times stronger than existing concrete in order to reduce the thickness of the wall structures by 75%. That is one of the considerations necessary in order to make the storage concept commercially viable. Research organization SINTEF will work for example on reinforcing the concrete with thin steel fibers instead of the normal steel rebar, says Tor Arne Martius-Hammer at SINTEF Building and Infrastructure.

Subhydro has teamed up with global consultant COWI, offshore EPC specialist Kvaerner, and hydropower specialist DynaVec. The team is also working with scientific experts from three institutes at SINTEF: SINTEF Energy Research, The Norwegian Marine Technology Research Institute MARINTEK, and SINTEF Building and Infrastructure.